1. Field of the Invention
The present invention relates to a power unit with an internal combustion engine having an auxiliary machine rotated by a transmission mechanism and a crankcase which houses the transmission mechanism and the auxiliary machine and to which the auxiliary machine is fitted, and a motorcycle which has the power unit.
2. Description of Background Art
It has been known that an oil pump of an internal combustion engine is housed in a space formed by a crankcase (for example, see JP-A No. 2004-143952 ). In the case where the oil pump is rotated by a transmission mechanism with an endless chain, a driven sprocket with the endless chain wound around it is fitted to the drive shaft of the oil pump.
When the oil pump is fitted to the crankcase with the driven sprocket fitted to the drive shaft of the oil pump, first the endless chain wound around the drive sprocket should be wound around the driven sprocket and then, while keeping this condition, the oil pump should be fitted to the crankcase with bolts or the like, so oil pump fitting work is troublesome.
A method of making oil pump fitting work easier may be to fit the driven sprocket with the endless chain wound around it to the drive shaft of the oil pump through an opening made in the crankcase after fitting the oil pump to the crankcase. In this case, if all the driven sprocket is exposed inside the opening when viewed from the axial direction of the crank shaft, it would be easy to fit the driven sprocket to the drive shaft but the opening should be large enough, so the rigidity of the crankcase would deteriorate.
Furthermore, if the endless chain which drives the oil pump is wound around the drive sprocket which is fitted to the crank shaft, there should be space for the endless chain between the crank shaft and the oil pump drive shaft and thus the size of the crankcase should be large around the crank shaft and also the opening should be large, so the rigidity of the crankcase would deteriorate.